Cereus
Cereus is a genus of large, columnar, night-flowering cacti native to South America, ranging from tall tree-like species to shrubbier clustering forms. Several members are among the most familiar and widely grown ornamental column cacti, valued for their statuesque ribbed stems, ease of culture and — in a few species — the strange, prized monstrose and crested forms that turn up in cultivation. The name Cereus (Latin for "torch" or "wax candle") is one of the oldest in cactus botany and once served as a catch-all for almost any columnar cactus before the group was split into the many genera we recognise today.
Description
Members of Cereus are ribbed, upright and often branching cacti that can range from knee-high shrubs to trees several metres tall. The stems are typically blue-green to grey-green — sometimes with a waxy, glaucous bloom when young — and divided into a modest number of prominent, sharp-edged ribs bearing spaced areoles. Spines vary from short and stubby to long and needle-like, and are usually less dense than in many other columnar cacti, so the ribs remain clearly visible.
The flowers are the genus's signature feature: large, funnel-shaped, usually white (occasionally flushed pink or cream), and opening at night to release a soft fragrance that attracts moths and bats. Each bloom lasts only a single night, closing by the following morning. Successful pollination is followed by fleshy, often colourful fruits — several are edible and pleasant, and in some species they are grown or gathered for eating.
Distribution
Cereus is South American in origin, centred on the eastern and central parts of the continent — Brazil, Argentina, Paraguay, Uruguay, Bolivia and neighbouring regions — with some species reaching the Caribbean. They grow in a range of warm, seasonally dry habitats, from thorny scrub and dry forest to rocky slopes and open grassland. Their tolerance and vigour have made several species popular far beyond their native range, and a few have naturalised in suitable frost-free climates around the world.
Notable species
- Cereus repandus — the Peruvian apple cactus, a tall tree-like species widely grown as an ornamental and hedge plant, with edible fruit.
- Cereus jamacaru — the Brazilian mandacaru, a large branching species and an icon of the Brazilian sertão.
- Cereus hildmannianus — a robust, near-spineless blue-green species common in cultivation (often sold under older names such as C. peruvianus).
- Cereus forbesii — a handsome blue-stemmed species, especially popular in its spiralled spiralis and monstrose forms.
- Cereus validus — a stout, strongly ribbed species from Argentina and neighbouring areas.
Cultivation
As a group, Cereus are among the easiest and most forgiving of the large columnar cacti, which is much of why they are so widely grown. Give them plenty of bright light — full sun suits most established plants — and a free-draining, mostly mineral mix. Water generously through the warm growing season once the soil has dried, then keep them much drier and cooler over winter to rest the plant and reduce the risk of rot. Most are fast-growing and can put on impressive height in a few seasons, so a stable, weighty pot and occasional repotting help keep a tall plant upright.
They are more cold-tolerant than many desert cacti but are not frost-hardy; protect from freezing and keep them dry in winter, when cold wet roots are the main danger. See Watering for seasonal technique. Because of their vigour, Cereus species are also one of the standard choices of rootstock for grafting slower or more delicate cacti.
Cultivars and hobby forms
Much of the collector interest in Cereus lies not in named cultivars but in the aberrant growth forms the genus throws so readily. Monstrose plants, with irregular, lumpy, disorganised growth, and crested (cristate) plants, whose growing point fans out into a wavy ridge, are both especially prized — the monstrose and spiralled (spiralis) forms of Cereus forbesii being long-standing favourites. These forms are usually propagated vegetatively to keep them true, and crests in particular are often grown grafted or given a little extra care, as they can be slower and more prone to rot than normal growth. See Grafting and Propagation — cuttings.
Propagation
Cereus propagate very easily. Cuttings of stem sections root readily once the cut surface has been allowed to callus for a week or more before potting into a barely moist mineral mix — see Propagation — cuttings. The species also grow quickly and reliably from seed, which germinates well with warmth and humidity; this is the usual route for producing large numbers of plants and for seed-grown rootstock (see Propagation — seed). Offsets and side branches, where produced, can be removed and rooted in the same way as cuttings (Propagation — offsets).
Common problems
- Rot — the main killer, almost always from cold, wet conditions or a poorly draining mix, especially over winter; softening and browning usually starts at the base.
- Etiolation — too little light produces thin, pale, weakly ribbed growth that spoils the plant's form and stability.
- Corky scarring and sunscald — sudden exposure to intense sun after a dull spell can scar the skin; acclimatise plants gradually.
- Pests — mealybugs (white fluff in areoles and among roots) and red spider mites are the usual offenders; see Pests and diseases.
See also
- Cereus repandus · Cereus jamacaru · Cereus hildmannianus · Cereus forbesii
- Grafting · Soil and potting mix · Watering · Propagation — cuttings · Propagation — seed